CD4 and Parkinson disease: Compared to that in HCs, the percentage of CD4+ T cells among lymphocytes was slightly lower in PD patients, but this difference was without statistical significance [32.60% (27.60–41.95%), 95%CI (29.85, 40.10%) vs. 35.65% (26.50–48.4%), 95%CI (29.05, 41.14%), P = 0.703, Figure 2A].